Abstract

The effect of Si doping on the structural quality of wurtzite GaN layers grown by molecular beam epitaxy on AlN buffered (111) Si substrates is studied. The planar defect density in the grownGaN layer strongly increases with Si doping. The dislocation density at the free surface of GaN significantly decreases when Si doping overpasses a limit value. Si doping affects the misorientation of the subgrains that constitutes the mosaic structure of GaN. The increase of the planar defect density and out-plane misorientation angles of the GaN subgrains with Si doping explain the decrease of dislocations that reach the free surface of GaN. A redshift in the photoluminescence spectra together with a decrease in the c-axis lattice parameter as the Si doping increases point to an increase in the residual biaxial tensile strain in the GaN samples.